1. Field of the Invention
The invention relates to a process for operating an injection molding machine with a stationary mold platen or die plate on a machine bed and with a movable die plate which are lockable during the injection process via magnetic closing elements. The invention further relates to a corresponding device for carrying out the process.
2. Description of the Prior Art
A closing unit for an apparatus for the injection molding of thermoplastics is already known from German reference DE 37 15 160 A1. In order to increase or generate the mold closing pressure at the end plate and/or at a portion of the pressing plunger facing the end plate, this closing unit is provided with at least one electromagnet by which the mold closing pressure is generated.
Furthermore, European reference EP 0 669 198 A1 discloses an injection molding apparatus with a core which is fastened to a stationary base plate and an outer mold which is fastened to a movable base plate. Magnet arrangements are attached at both sides of the outer mold to increase the closing force, and have adhesive surfaces. In the closed position, these adhesive surfaces contact armature surfaces on armatures fastened at the stationary base plate. The armature surfaces are formed of ferromagnetic material.
Both known injection molding devices have tie bars along which the movable die plate is guided.
A two-platen machine in which the closing force is applied so as to be controlled by electromagnets is known from European reference EP 0 544 903.
It is disadvantageous that the magnetic devices are arranged directly in the die plates. In this arrangement, the magnetic flux also flows through the die and, as a magnetic parallel connection point, magnetically operating actuators, such as valves of installed hot nozzles, are operatively impaired or not operable at all.
Further, the installation of the magnet coils in the die plates reduces the effective magnet flux surface and accordingly the possible closing force which can be generated.